Position limit switch



May 22, 1962 R. BACCHI 3,036,167

POSITION LIMIT SWITCH Filed Oct. 29, 1959 2 Sheets-Sheet l F/6 VENTOR.RA) 5 CH/ ATVTOPNEVS y 22, 1952 R. BACCHI 3,036,167

POSITION LIMIT SWITCH Filed Oct. 29, 1959 2 Sheets-Sheet 2 53 F/6 5 Far6664 63 48 46 INVENTOR. RA V 8A 601/ A T TOPNEVS United States Patent3,036,167 POSITION LIMIT SWITCH Ray Bacchi, San Bruno, Calif., assignorto Baldwin-Lima- Hamilton Corporation, a corporation of PennsylvaniaFiled Oct. 29, 1959, Ser. No. 849,537 4 Claims. (Cl. 20038) The positionlimit switch is useful especially with a valve actuator such as is shownin my copending application entitled Electro-Manual Operator, filedAugust 25, 1958, Serial No. 757,035, and assigned to the assigneehereof. In that environment, a rising stem valve is actuated by anelectric motor and means are provided for stopping the motor at theopposite ends of the valve stroke. The motor, depending upon theelectrical connections, is either stopped completely at the end of eachstroke, is slowed down immediately before the stop and then is stoppedor is automatically reversed at the end of the stroke. Various switchingmechanisms accomplish the electrical changes necessary to control themotor. The present invention has to do with an actuatorcontrolledposition limit switch suitable especially for use in the indicatedenvironment.

An object of the invention is to provide a position limit switch whichis eflective to give a precise and accurate positional control of thedevice being actuated.

Another object of the invention is to provide a position limit switchwhich while giVing precise control can be utilized in an environment inwhich there is a very great speed reduction between the electric drivingmotor and the device being controlled.

Another object of the invention is to provide a position limit switchthat can readily be set by the user at any selected actuating positions.

Another object of the invention is to provide a position limit switchwhich will retain its adjustment or setting indefinitely withoutdifiiculty.

Another object of the invention is to provide a position limit switchthat is effective despite adverse ambient conditions, such as vibration,shock and the like.

Another object of the invention is to provide an improved position limitswitch.

Other objects, together with the foregoing, are attained in theembodiment of the invention described in the accompanying descriptionand illustrated in the accompanying drawings, in which:

FIGURE 1 is a diagrammatic showing of the position limit switch of theinvention installed in connection with a typical valve actuator havingan electric motor drive.

FIGURE 2 is a side elevation of the position limit switch itself.

FIGURE 3 is a view similar to FIGURE 2, with the parts in a dilferentposition.

FIGURE 4 is a view similar to FIGURES 2 and 3, with the parts in a stilldifferent position.

FIGURE 5 is a plan of the switch as shown in FIG- URE 2.

FIGURE 6 is a cross-section, the plane of which is indicated by the line66 of FIGURE 5.

FIGURE 7 is a developed cross-section, the planes of which are indicatedby the lines 77 of FIGURE 2.

FIGURE 8 is an exploded, isometric View showing the relationship of theparts especially indicated in FIG- URE 7.

While the'position limit switch is susceptible of use in widelydifferent environments and under different circumstances, it hassuccessfully been incorporated in a valve actuator 5 such as indicatedin FIGURE 1 which includes a housing 6 enclosing the rising stem 7 of avalve 8. The actuator 5 includes a rotary member 9 such as an axiallyfixed nut engaging a threaded stem 7. By

3,35,1l57 Patented May 22, 1962 its rotation, the nut moves the valvestem. Rotation of the nut 9 is accomplished by an electric motor 11 receiving its power from mains 4, 1'2 and 13 through an electrical controlbox 10. The actuator 5 is provided with a shaft 14 emerging from thehousing and rotating in unison with the operation of the motor 11 sothat the position of the shaft 14 is indicative of the valve position.

The arrangement is such that the shaft 14 makes a very large number ofrevolutions for the complete travel of the valve stem so that theinstantaneous position of the shaft 14 reflects with considerableaccuracy the corresponding position of the valve 8.

Pursuant to the invention, the actuator 5 is provided with a bracket 16carrying a base or housing 18 for the position limit switch itself.Preferably, this is a body molded of plastic in two parts, an upperportion 19 and a lower portion 21. These portions are fastened togetherat intervals by separate through bolts 22 and nuts 23. Suitablyjournalled in the body 18 is a drive shaft 24 preferably extending onopposite sides thereof so that a drive wheel 26 can be installed oneither projecting end of the shaft 24 to mesh with a gear wheel 25 onthe shaft 14, depending upon the particular installation. The shaft 24is thus rotated in time with the shaft 14.

A worm gear 27 is fastened on the shaft 24 which is kept appropriatelypositioned within the housing 18 by collars 28 for carrying the shaftthrust. Also journalled in the housing 18 but disposed at right anglesto the drive shaft 24 is a first driven shaft 31. The shaft has arelatively large diameter and within the housing carries a first drivengear 32 meshing with one side of the worm 27. The gear 32 has a set orpredetermined diameter so that the shaft 24 drives the shaft 31 at apredetermined ratio. The shaft 31 carries substantially identicalmechanisms on its opposite ends outside :of the casing 18 so that adescription of one mechanism applies equally to the other. i

As especially indicated in FIGURE 7, one end of the shaft 31 after ithas emerged from the casing 18 is formed to afford a relatively flat end34 and to have a peripheral flange 36. Freely journalled on the enlargedportion of the shaft 31 is one of a pair of first cams 37 and 38 havinga cam track 33 on its periphery and being provided with an internal gear40. This is all preferably molded of plastic. The cam 37 normally freelyabuts the flange 36 and so is held against axial displacement in onedirection.

At the end of the shaft 31 there is provided a plate 41 preferablymolded of plastic and having a peripheral shoulder 42 in abutment withthe cam 37. Journalled in the plate 41 is a pinion shaft 43 at one endcarrying a pinion 44 meshing with the internal gear 40. The other end ofthe pinion shaft 43 carries a tool engaging means 46 so that the pinionshaft '43 can readily be rotated. The plate 41 is assembled to the shaft31 by a pair of machine screws 48 engaging threads in the enlarged endof the shaft 31.

When the machine screws 48 are in relatively loose engagement, the userby engaging a tool with the end of the pinion shaft 43 and appropriatelyrotating the shaft thus revolves the pinion 44. Since the plate 41 isheld against rotation relative to the driven shaft 31 by the two machinescrews 48, the cam 37 is necessarily rotated. This cam preferably has acontour substantially as shown in FIG- URE 3 with a depression 50interrupting the otherwise uniform cam track 39. The pinion shaft 43 canbe revolved to locate the depression 50 in any desired polar positionrelative to the shaft 31.

After the rotary or polar adjustment is made, the machine screws 48 aresuitably tightened. This clamps the cam 37 between the shoulder '42 andthe flange 36 and V clockwise direction in FIGURE 4, for example.

may also clamp the pinion 44 between the flat face 34 and thecorresponding portion of the plate 41;. Both the cam and the pinion maybe clamped or either one may be clamped frictionally in order that thecam track 39, after adjustment, will be firmly fixed relative to theshaft 31.

Mounted on the base or housing 18 (FIGURE is a pair of electricalswitches 51 and 52. These switches are of a standard kind and includeoperating buttons 53 spring-pressed outwardly of the switch casings 54.Since the instant device is preferably symmetrical, a'sirnilar pair ofswitches .56 and 57 is mounted at the other side of the housing, therebeing provided through bolts 59 and nuts 61 to hold all of the fourswitches in position. While the electrical switching arrangements can beset up in various different ways, the switches 51 and 52 as well as theswitches 56 and 57 serve as pilot switches acting through cables 60 and62 to operate the controls in the control box It) so that the motor 11can be selectively stopped; for example, at the opposite extremes oftravel 1 of the rising stem.

It is preferred that two of the switches, for example, 51 and 52, beactuated substantially simultaneously. For that reason, there isprovided a vtu'de switch lever 63 at one side of the housing 18. Thisswitch lever is mounted on a spindle '64 and is retained by an end lock66 so that the lever 63 can rock about the spindle 64 in a small arc.The contour of the lever 63, which is relatively stiff, is such that oneportion 67 of the lever is approximately radial with respect to thespindle 64 and affords means in abutment with the buttons 53. When thespringpressed buttons 53 are normally urged outwardly of the casings 54,the switch lever 63 is moved in a path, in a When a superior forceovercomes the springs in the switches 51 and 52, the lever 63 can berocked in a counterclockwise direction.

Pursuant to the invention, there is provided means for interrelating theswitch lever 63 with the cam 37. This is accomplished by making the widelever 63 of an offset shape to provide a cam follower 68 designed tocontact the cam track or surface 39. During the clockwise rotation ofthe cam 37, the cam track 39 normally urgesthe lever 63 to the left inFIGURE 3 and depresses the two buttons 53 of the switches 51 and 52.When the cam 37 has rotated sutficiently to bring the depression 50 inthe vicinity of the follower =68,'the spring behind the buttons 53 ofthe switches 51 and 52 is sufficient to rock the lever 63 into theposition shown in FIGURE 4.

Since the first cams 37 and 38 are rotated through the worm 27 in timewith the rotation of the motor 11, the

cam 37 makes one revolution for each predetermined.

number of revolutions of the motor 11. After a plurality of revolutionsand at a predetermined time, the switches 51 and 52 are moved from theirdepressed position to their projected position. Under normalcircumstances,.if

this actuation of the switches occurred each cam revolution, it would bemuch too frequent for the total travel of the valve stem 7. Yet, the.large amount'of movement is elfective'to afford a fine degree ofcontrol.

In order that only a certain rotation and not every rotation of thefirst cam 37 (and similarly with the first cam 38 in conjunction withthe switches 56 and 57) will be effective upon the switchesSl and 52,additional mechanism is provided. Mounted in the housing'ls is a see-0nd driven shaft'71 parallel to the first driven shaft 31.

The shaft 71 within the housing 18 carries a second driven gear 72meshing with the worm' 27. The circumference or pitch diameter of thesecond drivengear 72 is different than that of the first driven gear 32and preferably is larger so that for each complete revolut'lon of thefirst driven shaft 31 there is only; a partiaL although nearly complete,revolution of the second driven shaft 71.-

The second driven'shaft 71 projects on opposite sides 1 of the. housing18 and is provided on its exposed portions l with a pair of second earns73 and 74. These are identical not only with each other but also withthe first earns 37 and 33 except for the cam surfaces. The descriptionof the operation of one of the second earns 73 is therefore applicableequally to the other since the opposite sides of the device aresymmetrical. The contour of the second cam 73 is preferablysubstantially'as shown in FIGURE 3 and includes a generally circular camface 76 with a projection 7 7 extending therefrom.

Mounted on the housing 18 partially in the path of the projection 77 isa latch lever 7 8. This at one end encompasses a spindle 79 projectingfrom the housing 18 and is retained in position by a lock 81. One end'82 of the latch lever 78 is bent to underlie a pin 83 so that the latchlever acts as its own spring. The latch lever 78 not only lies in thepath of the projection 77 but also extends over the first cam 37 and hasan end 84 in proximity to the upper end 67 of the switch lever 63.

As shown in FIGURE 2, when the first and second cams are in the positionillustrated, there is restraint on the switch lever 63 by the first cam37, and there is preferably slight clearance between the switch leverand the end of the latch lever 78. .When the cams have advanced to andslightly past the position shown in FIGURE 3, the

latch lever 78 lifts out of the path of the switch lever 63 That is,they are in appropriate polar positions so that the projection 77 liftsthe latch lever 78 and restores it and repeatedly does so while thedepression 50 of the first cam 37 is in various positions, but alwaysaway from the follower 68. Also, the depression 50 may'underride thefollower 68 repeatedly, but always when the projection 77 is in variouspositions out of contact with the latch lever 78. After a large numberof revolutions-theca-ms are again in phase. Then the follower 68 is ableto drop into the depression 50 when the latch lever 78 is lifted and topermit the spring-pressed buttons 53 of the switches 51' and 52 to beactuated.

If the cams continue to rotate in their previous directions for anyreason, such as manual overriding control, the projection 77 and thedepression'50 again get out of phase so thatsubsequent rotations of thecams do not cause switch actuation. Normally, switch actuation stops themotorwhich is subsequently manually reversed. Upon reverse rotation ofthe cams with reversal of the driving motor 11, the switch lever 63follows a reverse movernent restoring the switches 51 and 52 to theiroriginal condition and the latch lever 78 drops back into its latchingposition. 1

Normally, the ratio of the gears '32 and 72 is so chosen and therelative phasing or polar positions of the first cam 37 and second cam73 are so chosen that it is only after a large number of revolutions ofthe motor 11 or of the rant 9 on the valve stem that there is anactuation of the switches 51 and 52. Similarly, and at theother end ofthe stroke, it is only after. alarge number of revolutions of the nut 9that thee-ams 38 and 74 actuate the switches 56 and 57. The adjustmentof the pair of first cams and of the pair of second. cams canreadilybealtered by the user at any time simply by loosening the machine screws48 and rotating the particular pinion shaft 43. Thus, the

does not inadvertently cause the switches to operate. The mechanismwhich especially requires enclosure and may involve lubrication, such asthe driving and driven gears, is located within the housing whereas themechanism which involves adjustment is readily available from theexterior. The entire mechanism is simple and light and permits of a widevariety of control conditions with easily changed yet firm adjustments.There has thus been provided a substantially improved position limitswitch.

What is claimed is:

1. A position limit switch comprising a housing, a first driven shaftpassing through and projecting from said housing, a second driven shaftpassing through and projecting from said housing parallel to said firstdriven shaft, a first gear of one diameter within said housing and onsaid first driven shaft, 21 second gear of another diameter within saidhousing and on said second driven shaft, a drive shaft extending intosaid housing, a driving gear within said housing and on said driveshaft, said driving gear meshing with said first gear and with saidsecond gear, a first pair of cams, means for mounting said first cams onsaid first shaft for various polar positions thereon, a second pair ofcams, means for mounting said second cams on said second shaft forvarious polar positions thereon, switches on said housing, a pair ofswitch levers pivoted on said housing in actuating position with saidswitches, means on one of said switch levers in engagement with one ofsaid first cams, means on the other of said switch levers in engagementwith the other of said first cams, a pair of latch levers pivoted onsaid housing for movement into and out of latching position withrespective ones of said switch levers, and means on said latch leversrespectively in engagement with said second cams.

2. A position limit switch comprising a housing, a first driven shaftmounted in said housing, a second driven shaft mounted in said housing,a first gear of one diameter on said first shaft, a second .gear ofanother diameter on said second shaft, a drive shaft, a driving gear onsaid drive shaft and meshing with said first gear and said second gear,a first cam, means for mounting said first cam on said first shaft forvarious polar positions thereon, a second cam, means for mounting saidsecond cam on said second shaft for various polar positions thereon, aswitch on said housing, a switch lever, means for mounting said switchlever on said housing for abutment with said switch and with said firstcam, a latch lever, and means for mounting said latch lever on saidhousing for interengagement with said switch lever and for abutment withsaid second cam.

3. A position limit switch comprising a base, a switch on said base, aswitch lever, means for mounting said switch lever on said base forabutment with said switch, means for urging said switch lever away fromsaid switch, a rotary first cam on said base for moving said switchlever toward said switch, a latch lover, means for mounting said latchlever on said base for movement into and out of the path of said switchlever, means for urging said latch lever into the path of said switchlever, a rotary second cam on said base for moving said latch lever outof the path of said switch lever, and means on said base for rotatingsaid first cam and said second cam at different relative rates.

4. A position limit switch comprising a base, a switch on said base, aswitch lever, means for mounting said switch lever on said base formovement in a first path between one position in actuating abutment withsaid switch and another position away therefrom, a rotary first cam onsaid base for moving said switch lever in one direction along said firstpath, spring means for urging said switch lever in an oppositedirection, a latch lever, means for mounting said latch lever on saidbase for movement in a second path between one position intersectingsaid first path and another position away therefrom, a rotary second camon said base for moving said latch lever in one direction along saidsecond path, spring means for urging said latch lever in an oppositedirection, and means on said base for rotating said first cam and saidsecond cam at different relative rates.

References Cited in the file of this patent UNITED STATES PATENTS1,643,852 Linstow Sept. 27, 1927 1,856,832 Halvorson May 3, 19321,964,909 Garity July 3, 1934 2,554,545 Winder May 29, 1951 2,592,2 7Bradley Apr. 8, 1952 2,594,911 Goff Apr. 29, 1952 2,857,784 BrailsfordOct. 28, 1958 2,925,478 Yamasaki Feb. 16, 1960 2,933,568 Harada Apr. 19,1960

